The present invention relates to hydrostatic transaxle assemblies, and more particularly, to such assemblies which have the capability for the operator to select from among various operating modes.
Certain vehicles, such as lawn and garden tractors, have used hydrostatic transaxle assemblies for transmitting engine torque to a pair of ground-engaging drive wheels to propel the vehicle. A typical transaxle assembly which has been used commercially includes a variable displacement hydraulic pump, such that the ratio of pump output flow to pump input speed (engine speed) could be infinitely varied by the vehicle operator. This ability to infinitely vary the output-input ratio, without interrupting torque transmission, makes transaxle assemblies greatly preferred over conventional clutch and gear transmission arrangements for vehicles of the type referred to above.
Vehicles which utilize transaxle assemblies frequently encounter operating conditions in which one of the drive wheels has less traction than the other drive wheel. It has long been recognized by the manufacturers of such vehicles that it is desirable to provide the operator of the vehicle with some type of control arrangement for effectively dealing with such loss of traction situations. At the same time, however, it is recognized that under most operating conditions, the vehicle must be able to have "normal differentiation" between the two drive wheels, i.e., it must be possible for the two drive wheels to be driven at substantially different speeds, such as during a sharp turn.
In addition to dealing with the loss of traction situation, there are various other operating conditions which occur with such vehicles. For example, it is normally desirable for vehicles of this type to have some sort of parking brake to be applied only when the vehicle is at a standstill, and it is especially desirable to incorporate such a parking brake into the transaxle assembly to be used to propel such a vehicle.